The invention relates to a device for inscribing materials with a laser.
The text, Walter W. Weinfurtner, xe2x80x9cLicht schreibtxe2x80x94Beschriften mit dem Laser in der Industrie: Grundlagen und Einsatzgebietexe2x80x9d, Expert-Verlag 1995 (Kontakt and Studium; Volume 479) disclosed the principle and the basic structure of a laser inscriber, consisting of a solid-state laser with a laser head with, for example, an optical path, on which the individual optical components are mounted in such a way as to ensure temperature stability and mechanical stability.
In the laser head of the solid-state laser there is a resonator, which consists of a so-called pump chamber, two reflectors and an acoustic-optical switch, a so-called Q-switch. In the pump chamber there is a YAG crystal rod and one or several krypton arc-lamps whose light is reproduced in the crystal rod which emits light with a certain wavelength at both ends. This light is reflected by the two reflectors back into the crystal rod, whereby the reflector at the rear end of the resonator reflects around 99.9%, whereas the front reflector transmits 12% and thus forms the operating beam. The Q-switch interrupts the operating beam up to 40,000 times per second and thus produces output peaks up to 1000 times the continuous wave laser operation.
Furthermore, the resonator contains a mechanical switch (shutter) for interrupting the laser beam and a support, in which a mode filter is set to suit the specific application, in order to achieve higher beam quality (including, for example, in basic mode operation). In a beam spreader, the laser beam leaving the resonator is spread by a factor of 2 to 10. The spread laser beam is refracted in a refraction unit by means of two galvanometer reflectors in the x and y directions and focused on a work-piece by means of a flat field focusing lens.
Further, components of the existing laser inscriber are a computer for driving a control unit which controls the refraction device, a Q-switch driver and a power pack. An additional, costly cooling device is provided for cooling the pump chamber.
The existing laser inscriber is formed as a laser installation with an x-y stage table, a round switching table with input and output tunnel and possibly a twin- head configuration, like when it is used as a solid-state laser for material processing too, i.e. for separating, joining, boring and the like with high laser power, whereby the laser is additionally to be connected to a power supply cabinet and possibly to an external heat exchanger. A laser inscription installation of this nature, as is also the object of DE3318768A1, has a bulky construction and can therefore only be used at fixed locations. Such an installation also has a considerable power consumption and a low rate of efficiency, as a large proportion of the power must be removed by means of the cooling device in order to ensure problem-free operation.
A laser installation of this nature has considerable dimensions and requires a water supply for cooling the laser. It also requires a three-phase current connection with a power consumption of around 8 kW. This laser installation requires extensive maintenance, as the presence of the water supply means that an ion exchanger and a particle filter are necessary. High lamp consumption and considerable wear and tear of the pump chamber must also be taken into consideration.
As can be seen from DE3318768A1, a laser inscription installation of this nature also requires a costly alignment device and a refraction head containing numerous optical components whereby there is a scattering lens and a converging lens of the widening lens system, reflectors and the like. These make the manufacture, maintenance and operation of the existing laser inscription installation expensive.
JP-A-08 001 999 discloses a further laser inscription installation which has a low power laser and a refraction unit. By means of this installation, an image is produced on a photo-sensitive upper surface of a drum through electro-static charging. For this purpose, the drum is exposed to a laser beam. In order that the entire upper surface of the drum can be exposed, the drum rotates around its rotation axis. In addition, the refraction unit is positioned in the longitudinal direction of the drum along the upper surface of the drum in such a way that it can move.
The existing device is used in a laser printer in order to inscribe paper. For this purpose, toner is applied to the drum, whereby the toner only sticks to the electrostatically charged areas of the drum. In order to apply the toner to the paper, the paper is then passed over the drum.
The disadvantage of the existing device is that it requires a costly and precise guide facility, in order to ensure a sufficient relative movement between the drum and the refraction unit in such a way that the entire upper surface of the drum can be reached by the laser beam. Among other things, this necessitates a costly alignment device to ensure that the laser beam, by means of the refraction unit, reaches each position on the upper surface of the drum.
The precise guide facility also means that the existing device must be installed at a fixed location. In order to use the existing device at another location, it must first of all be dismantled, transported to the other location and then put together again. This necessitates an enormous amount of resources which results in high costs. In principle, therefore, the existing device can only be used at a fixed location.
Furthermore, with the existing device it is not possible to produce engravings and inscriptions on objects by means of material vaporization. This is only possible when using a high-power laser. If such a high-power laser were used with the existing device, this would mean that the dimensions of the installation would be greatly increased.
It is an object of the present invention to create a device for inscribing virtually any material with a laser with considerably smaller dimensions and considerably lower weight as well as optimum handling and the greatest possible mobility whereby this is achieved with low manufacture and operating costs, as well as low power consumption and low maintenance requirements.
The solution according to the invention creates a mobile device for inscribing objects with a solid-state laser, whereby this device is characterized by small dimensions and low weight, as well as by simple construction. The form of the inscription device can differ both in relation to data input and in relation to the output head. It can also be connected to any peripheral devices such as a digital video camera, a CCD image sensor, a scanner and the like.
By bringing together several respective components in at least one package, the configuration of the inscription laser can correspond to an application-oriented structure.
In a first embodiment of the solution, according to the invention, the inscription device consists of a hand-held device which contains a refraction unit and a solid-state laser and is connected by means of a cable connection to a support device which has a control unit and a power pack, for example, an accumulator and/or a main unit. In addition, there is an interface for connecting the control unit to an external control and/or input unit.
In a second embodiment of the solution, according to the invention, the hand-held device contains only the refraction unit and is connected by means of a glass fiber cable to a support device which contains the solid-state laser, the control unit and the power pack. In this case also, there is an interface for connecting the control unit to the external control and/or input unit.
In a third embodiment of the invention, all the components can be brought together in one package which is formed as a hand-held device or a desk-top device.
In all three embodiments of the invention, the dimensions are so compact that the hand-held device can, for example, be formed as a gun and the support device can be housed in a package which can be attached to a user by means of a waist and/or shoulder strap. With this construction, maximum mobility is achieved and this enables the user to carry out laser inscriptions at any location independently of a power supply cabinet and the like.
It is particularly advantageous if the hand-held device is connected to a sensor unit, for example a scanner, a video camera or a digital camera. For example, this enables an image to be recorded with the sensor unit, and to be produced on an object by means of the hand-held device. Therefore, the device is preferably suited for the administration of a warehouse used for the storage of goods which have a bar-code for identification purposes. For example, the bar-codes are read by means of the scanner, transmitted to a computer located in the hand-held device or to another superordinate central computer, where they are processed. Should it ever be necessary to change the bar-code, the old bar-code can easily be made indecipherable, or removed by means of the hand-held device and the new bar-code can be put on the goods.
In an advantageous embodiment of the solution according to the invention, there is a recording unit for the objects which are to be inscribed, whereby this recording unit contains a distance-measuring device for emitting a distance reading which controls the focusing of the laser beam. The recording unit also contains a switching device for releasing the laser beam when the object to be inscribed is correctly positioned. As an alternative, there is a mechanical catch for static focusing of the laser beam.
The inclusion of a recording unit, for objects to be inscribed, ensures reliable positioning of the object in the focal plane of the laser beam. It also ensures reliable operation of the inscription device.
As an alternative or additionally, there is a lens system, for example a lens system of an auto-focus camera, for the purpose of adjusting the focus distance.
In a preferred embodiment of the invention, in order to ensure maximum mobility of the unit, the control unit is connected to an external control and/or input unit wirelessly by means of a radio, infra-red or ultrasound transceiver.
The control unit and possibly components of the power pack are preferably composed from foil circuits using SMD technology. They are therefore particularly suitable for a compact structure and housing in component packages which can be carried on the body of the user.
In order to ensure the smallest possible dimensions and a maximum efficiency rate, the laser consists of a solid-state laser which is pumped longitudinally with a laser diode, whereby this solid-state laser contains a laser bank with a laser crystal, a Q-switch, a highly-reflecting resonator reflector and an output reflector. The laser crystal thereby preferably has no tension birefringence or has a tension birefringence which is as low as possible, and in addition it has high fluorescence durability and the smallest possible dimensions.
The solid-state laser can be equipped with an active Q-switch, i.e. with an opto-acoustic crystal, or with a passive Q-switch and a laser diode, which among other things, is driven in pulsed operation.
The efficiency rate of the laser diode is preferably as high as possible. In order to ensure that this efficiency rate remains stable, the laser diode is cooled with a cooling component, for example a Peltier component. It is provided that both the laser diode driver and the Peltier driver are positioned either in the hand-held device or in the support device. The term xe2x80x9cdriverxe2x80x9d is used here to denote the corresponding circuit board of a component.
The individual laser components are preferably in a very compact arrangement in relation to one another, in order to achieve minimum dimensions and thus ensure mobile operation.
In particular, short resonator geometry is used, which means that very short laser pulses, and thus, a high pulse peak output are achieved. In order to ensure a configuration that is as compact as possible with small external dimensions, the short resonator geometry is preferably achieved by means of a folded optical train brought about by an appropriate reflector configuration, for example, two reflectors positioned at 45xc2x0 to the axis of the beam.
In addition, the device has another lens system for spreading the beam, preferably by means of two lenses. Alternatively or additionally, the beam is spread by means of a further reflector system comprising at least two reflectors, whereby this reflector system preferably also has a folded optical train through multiple reflection.
In a preferred embodiment of the invention, polarizers are provided, in order to generate polarized laser light. This light can, however, also be generated through the laser crystal itself. In this way, it is possible to increase the diffraction efficiency rate of an acoustic-optical Q-switching component. This is particularly advantageous because the device according to the invention preferably has at least one lens system with a high diffraction efficiency rate, in particular a crystal, whereby this lens system efficiently interrupts the laser process in the resonator at the same time as there is low high-frequency power input.
In order to further increase the compactness and to minimize the weight, the components of the device according to the invention are manufactured from fiber reinforced materials, ceramics or synthetic materials. In addition, the lens systems are put together and/or are secured by means of sticking.
In order to ensure a fast, accurate and cost-effective drive for the refraction unit, in a preferred embodiment of the invention, the motor of the drive unit, by means of which the refraction unit is adjusted, is constituted by a drive unit of a read/write head of a data storage unit, in particular a magnetic or optical data storage unit. However, the invention is not restricted to this type of drive unit. Moreover, conventional drive units, for example galvanometer scanners, can also be provided as drive units for the refraction unit.